Brush and holder assembly



BRUSH AND HOLDER ASSEMBLY Filed Oct. 6, 1961 -i I x 55 L 4 :32 8 44 Y 4 llll INVENTOR. 5 Cos-ms flVGEP/NOS F7 TTOP/VE Y v out hereinabove.

force which changes very United States Patent 3,188,407 BRUSH AND HOLDER ASSEMBLY Costas Avgerinos, Wilton, Conn., assignor to United Arrcraft Corporation, East Hartford, Conn., a corporation of Delaware Filed Oct. 6, 1961, Ser. No. 143,384 4 Claims. (Cl. 200-24) in a binary digital code of the position of the disk shaft.

The brushes employed in these devices must have very small contact forces so that the wear on the disk as it rotates at high speeds is a minimum. Moreover, it is required that the contact force change very little even for relatively large deflections of the brushes. If contact of the brush with the disk is not maintained at all times, then an erroneous read out results.

'It has been suggested in the prior art that a brush assembly associated with a circle of coded segments, for example, be made up by a plurality of wires formed of conductive material which resiliently engage the elements of the circle. In response to rotation of the disk or of the brushes relative to the disk electrical outputs are produced in accordance with the pattern of the disk and the number and arrangement of the wire brushes. In most converters the output signals should be of a square waveform and there should be only a constant minimum voltage drop over the life of the brushes and segments. For

'these requirements to be met the brushes must always contact the surface of the disk even at high accelerations and under the low contact pressures which are necessary .to' prevent excessive wear. It is further necessary that stress in the wire owing to loading will remain well below the elastic limit of the material. Many of these converters of the prior art are miniaturized with the result that the requirement that the brushes of a group adapted .to contact a particular circle of segments be maintained in their lateral positions assumes great importance.

I have discovered that by making the brushes short a wire brush assembly can be made to have a high frequency response so that any bouncing of the brushes dies out very rapidly. I have discovered further that by employing relatively long wires to make up the brushes a relatively constant pressure over a wide range of brush deflection can be achieved. It will readily be apparent that these two requirements are inconsistent with each other.

I have invented a novel brush assembly which overcomes the disadvantages of brushes of the prior art pointed My brush assembly successfully fulfills the apparently inconsistent requirements for high frequency response and relatively constant brush pressure for a wide'range of deflections. My assembly is such that stress on the wires making up the brush under load is well below the elastic limit of the brush material. My assembly is so arranged that it provides a very small contact little even for relatively large deflection of the brush wires. My assembly ensures that contact of the brush wires with the coded portion is maintained even at high accelerations with the low contact pressures provided. My assembly is simple and inexpensive for the result achieved thereby. I

One object of my invention is to provide a brush assembly which is especially adapted for use in a high speed shaft position encoder.

Another object of my invention is to provide a brush assembly which overcomes defects of brush assemblies of the prior art.

A further object of my invention is to provide a brush assembly which ensures contact between the brush and an encoder disk even at high accelerations with low contact pressures.

Still another object of my invention is to provide a brush assembly which has a relatively constant spring pressure even for a relatively wide range of deflections of the brush.

A still further object of my invention is to provide a brush assembly which fulfills the apparently inconsistent requirements for a high frequency response and for constant contact pressure over a wide range of deflections.

Yet another object of my invention is to provide a brush assembly which is simple and inexpensive.

Other and further objects of my invention will appear from the following description.

In general my invention contemplates the provision of a brush holder assembly for a shaft position encoder or the like in which a stabilizer acts at a point along the length of the assembly brush wires, which provide plural contact with the code pattern. The action of the stabilizer provides a high frequency response for the wires while ensuring that the contact pressure is substantially constant over a relatively wide range of brush deflections. I provide my stabilizer with means for retaining the brush wires in position laterally of the pattern with which they are associated.

In the accompanying drawings which form part of the instant specification and which are to be read in conjunction therewith and in which like reference numerals are used to indicate like parts in the various views:

FIGURE 1 is a fragmentary plan view of a shaft position encoder with which my brush assembly may be used.

FIGURE 2 is a sectional view of the encoder shown in FIGURE 1 taken along the line 2-2 of FIGURE 1.

FIGURE 3 is a fragmentary sectional view of my brush assembly showing the assembly in its unloaded position.

FIGURE 4 is a graph illustrating the natural frequen cies of the wire beam (curVeA) and of the stabilizer (curve B), the phase opposition of which produces the vibration filtering effect or dampening.

Referring now to FIGURES l and 2, the shaft position encoder indicated generally by the reference character 10 with which my brush assembly indicated generally by the reference character 12 is to be used includes a shaft 14 carrying a disk 16 the surface of which is provided with a pattern 18 of segments 20 of conductive material. This pattern may be applied to the disk in any suitable manner known to the art such, for example, as by photoetching techniques or the like. It includes a number of rows of segments, two of which rows 22 and 24 are defined by broken lines in FIGURE 1 and an intermediate row 26 of conductive material providing connections to the adjacent rows 22 and 24. It will readily be appreciated that while I have shown only a portion of the coded pattern carried by the surface of disk 16, very nearly the entire surface of the disk is covered with the coded pattern. In the particular arrangement shown the rows 22 and 24 of segments 20 are arranged along the locus of a circle. It will be understood that they could, if desired, be linear in which case the converter 10 would be a linear position encoder. In operation of the encoder It) as shaft 14 rotates the segments 20 of the rows 22 and 24 move under two of my brush assemblies 12 to produce electrical outputs in a manner known to the art. It is, of course, possible that the disk could be stationary and the brush assemblies moved over the rows 22 and 24.

Each of the brush holder assemblies 12 includes a plurality of wires 28, the ends 30 of which are curved to contact the surface'fS of the disk 16. In the particular embodiment shown there are four wires 28 for each of the brush holder assemblies 12. Associated with each plurality of wires 28 is a stabilizer element 32 which overlies the wires. Any suitable means may be employed to hold. the brush assemblies 12 in positions at which the ends 30 of the group-of wires 28 can contact their associated rowof segments. In the holder illustrated in the drawings a support 34 is provided with a plurality of recesses 36 having inclined upper surface for receiving the a through these members. In fixing an assembly 12 in its position I place the stabilizer 32 and the wires 28 in the correct position and then force a wedge 42 in position in the recess 36 to clamp the wires and the stabilizer between the wedge and the inclined surface of the recess 36 in the support 34.

Referring to FIGURE 2, I so position the wires 28 and the stabilizer 32 within a recess 36 that the wires 28 extend for a distance L from the end of the support 34 to the point at which the wires contact the surface of the disk 16. Stabilizer 32 extends for a distance L from the end of support 34 to the point at which its end engages the wires 28 so that the wires extend for a distance L .from the end of the stabilizer to the point at which they contact the surface 18 of the disk 16.

The Wires 28 are made of a suitable resilient conductive of a revolution of the shaft 14. Electrical connections to the brushes may be made in any suitable manner known to the art.

Owing to the fact that the portions of the wires 28 extending from the end of the stabilizer 32 to contact the disk are relatively short, they have a higher frequency response than wires alone so that any bounce generated in the brushes dies out relatively rapidly. This is demonstrated by the curves in FIGURE 4 in which curve A illustrates the action of the brush wire beam in free state vibration, and curve B illustrates the action of the stabilizer beam in free state vibration. Because of the fact that'these two frequencies are different, they seldom will be found in phase andtherefore one will oppose the other at some instant thus producing the vibration filtering 'effec or dampening. Owing torthe fact that the over-all length of the assembly from the end of the support 34 to the point of contact of thebrushes with the disk is long the assembly can deflect over a relatively wide range withmaterial which preferably is of noble metal having a high tensile modulus. For the stabilizer 32 I employ a dimensionally stable high tensile modulus material having a low creep rate. Specific materials which can be employed for the stabilizer are a polycarbonate or polyester film. For

1 example, Lexan #100, which is the registered trade mark of the General Electric Company for a thermoplastic polycarbonate resin, may be used. Another suitable material is Mylar, which is the registered trademark of E. I. du Pont de Nemours & Company for a highly durable, transparent, water-repellant film of polyethylene terephthalate resin. I

I provide the stabilizer 32 of each of my brush assemblies 12 with a pair of downwardly bent ears 44 and 46 adjacent its free end. These ears 44 and 46 serve to retain the brush wires 28 in position laterally of the row of segments withwhich they are associated.

In one specific example of a brush assembly made. according to my invention, I take three contact WilfiS'ZS each 0.004" in diameter. As astabilizer I use a film of the material described'above having a thickness of 0.005 5" and a width of 0.050". I then assemble the wires and'the stabilizer in a recess 36 in the support 34 with the length L from the end of the support to the point of contact of the wires 0.200". The length L of the stabilizer from the end of the support to the end of the stabilizer is 0.130". The moduli of the materials are 11.5)(10 p.s.i. and 3.2 10 p.s.i., respectively.

In another embodiment of my invention, I use four contact wires of the type described in the first example in combination with a stabilizer 0.005" thick and 0.060"

trical signals as they contact segments. 20 in the course ferent from those of the wires.

out appreciable change in the force with which the wire brushes 28 contact the disk.

It will be appreciated that a change in the deflection at the end 30 of the wires results in a change in the resistive force exerted by the stabilizer on'the wires. Consequently, there is an increase in the structure rigidity of the assembly with increased tip deflections. I have also discovered that the stabilizer acts as a damping agent on the wires 28 since its harmonic characteristics are dif- The stabilizer and the wires, acting in combination, produce a theoretical fundamental natural frequency which is different from the natural frequency of either of the elements taken alone.

I have found that resonance at'this frequency is not distinguishable in operation of my brush assembly and I believe that this is a result of the damping force which should be exerted by the stabilizer'on the wires. I have found, further, that for the same tip force there occurs a -reduction in deflection of the tips'30 from that which would occur if no stabilizer were used. Consequently, the magnitude. of the maximum stress of the material is reduced.

It will be seen that I have accomplished the objects of my invention. 1 have provided a brush holder which overcomes the defects of brush holders of the prior art. My brush holder is especially adapted for use in a high speed shaft position encoder. My assembly ensures contact with a substantially constant force between the brush and its contact even at high accelerations. My assembly fulfills the apparently inconsistent requirements for high frequency response and for constant contact pressure over a relatively wide range of deflections.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of my claims. It is further obvious that various changes may be made in details within the scope of my claims without departing from the spirit of my invention. It is, therefore, to be understood that my invention is not to be limited to th specific details shown and described. Having thus described my invention, what I claimis: 1. A brush assembly for contacting a relatively movable conductive. area including in combination aplurality' of light elongated brushes of resilient conductive material, a support, means mounting said brushes on said support in intimate side-by-side relationship with a predetermined length of said brushes extending outwardly from said support to provide indepedently movable portions of said brushes remote from said support adapted'lig'htly to,con-' tact said relatively movable conductive area, an elongated resilient stabilizer element form of a material stiffer than 7 said brush material and means mounting said stabilizer element on said support with a length of said stabilizer element extending outwardly from said support to make contact with all of said brushes on the brush lengths. I

2. A brush assembly for contacting a relatively movable conductive area including in combination a plurality of light elongated brushes of resilient conductive material, a support, means mounting said brushes on said support in intimate side-by-side relationship with a predetermined length of said brushes extending outwardly from said support to provide independently movable portions of said brushes remote from said support adapted lightly to contact said relatively movable conductive area, an elongated resilient stabilizer element formed of a material stiffer than said brush material, and means mounting said stabilizer element on said support with a length of said stabilizer extending outwardly from said support to make contact with all of said brushes on a line extending across the brush lengths, said stabilizer length extending outwardly from said support being greater than half the length of said brushes extending out of said support.

3. A brush assembly for contacting a relatively movable conductive area including in combination a plurality of light elongated brushes of resilient conductive material, a support, means mounting said brushes on said support in intimate side-by-side relationship with a predetermined length of said brushes extending outwardly from said support to provide independently movable portions of said brushes remote from said support adapted lightly to contact said relatively movable conductive area, an elongated resilient stabilizer element formed of a material stifi'er than said brush material, means mounting said stabilizer element on said support with a length of said stabilizer element extending outwardly from said support to make contact with all of said brushes on a line extending across the brush lengths and depending ears formed on said stabi lizer adjacent the outboard brushes to restrain said brushes against lateral movement.

4. A brush assembly for contacting a relatively movable conductive area including in combination a plurality a line extending across of light elongated brushes of resilient conductive material formed with arcuate portions adjacent one end thereof adapted to engage said conductive area, a support, means mounting said brushes on said support in intimate side-by-side relationship with a predetermined length of said brush extending outwardly from said support with said arcuate portions being independently movable remote from said support and adapted lightly to contact said relatively movable conductive area, an elongated resilient stabilizer element formed of a material stitfer than said brush material and means mounting said stabilizer element on said support With a length of said stabilizer element extending outwardly from said support to make contact with all of said brushes on a line extending across the brush lengths, said length of said stabilizer element extending out of said support being greater than half the brush lengths extending out of said support.

References Cited by the Examiner UNITED STATES PATENTS 2,434,740 l/48 Glaser et al. 339-5 2,634,342 4/53 Baechler et a1 200-24 2,649,513 8/53 Luhn 200-24 X 2,716,684 8/55 Barnes 200-166 2,821,584 1/58 Monack et a1. 200-28 2,832,854 4/58 Doyle et al. 200-24 2,889,530 6/59 Straub et al. 339-5 2,902,522 9/59 De Oliveira 200-28 2,918,542 12/59 Bentley 200-24 X 2,967,216 1/ 61 Zablocki 200-24 FOREIGN PATENTS 323,187 7/20 Germany. 912,352 5/54 Germanty.

BERNARD A. GILHEANY, Primary Examiner. MAX L. LEVY, Examiner. 

1. A BRUSH ASSEMBLY FOR CONTACTING A RELATIVELY MOVABLE CONDUCTIVE AREA INCLUDING IN COMBINATION A PLURALITY OF LIGHT ELONGATED BRUSHES OF RESILIENT CONDUTIVE MATERIAL, A SUPPORT, MEANS MOUNTING SAID BRUSHES ON SAID SUPPORT IN INTIMATE SIDE-BY-SIDE RELATIONSHIP WITH A PREDETERMINED LENGHT OF SAID BRUSHED EXTENDING OUTWARDLY FROM SAID SUPPORT TO PROVIDE INDEPENDENTLY MOVABLE PORTIONS OF SAID BRUSHES REMOTE FROM SAID SUPPORT ADAPTED LIGHTLY TO CONTACT SAID RELATIVELY MOVABLE CONDUCTIVE AREA, AN ELONGATED RESILIENT STABILIZER ELEMENT FROM OF A MATERIAL STIFFER THAN 